2.1 Autoimmune Diseases
Autoimmune diseases are caused when the body's immune system, which normally defends the body against bacteria, viruses and other infective agents, attacks “self” tissue, cells and organs. The mobilization of the immune system against such self targets is termed autoimmunity. Although some autoimmunity is present in every individual, rigid control systems suppress the self-recognizing cells of the immune system to an extent that the autoimmunity is normally asymptomatic. Disease states arise when there is some interruption in the control system, allowing the autoimmune cells to escape suppression, or when there is some change in a target tissue such that it is no longer recognized as self. The mechanisms underlying these changes are not well understood, but have been theorized to be the result of aberrant immune stimulation in genetically predisposed individuals.
Autoimmune diseases can be organ specific or systemic and are provoked by differing pathogenic mechanisms. Organ specific autoimmunization is characterized by tolerance and suppression within the T cell compartment, aberrant expression of major-histocompatibility complex (MHC) antigens, antigenic mimicry and allelic variations in MHC genes. Systemic autoimmune diseases usually involve polyclonal B cell activation and abnormalities of immunoregulatory T cells, T cell receptors and MHC genes. Examples of organ specific autoimmune diseases are diabetes, cutaneous psoriasis, ulcerative colitis, hyperthyroidism, autoimmune adrenal insufficiency, hemolytic anemia, multiple sclerosis and rheumatic carditis. Representative systemic autoimmune diseases include systemic lupus, erythematosus, rheumatoid arthritis, psoriatic arthritis, Sjogren's syndrome polymyositis, dermatomyositis and scleroderma.
Also, while not having an autoimmune disorder, organ transplant recipients often experience similar symptoms and require similar therapies to autoimmune patients. Immune system attacks on the transplanted organ(s) can lead to organ failure or more serious systemic complications, e.g., graft-vs.-host disease (GVHD) in bone-marrow transplant recipients.
There is a clear need for improved strategies to treat autoimmune disorders and/or to modulate immune response. Currently, immune system disorders are treated with immunosuppressive agents such as cortisone, aspirin derivatives, hydroxychloroquine, methotrexate, azathioprine, cyclophsophamide and various biologics such as anti TNF antibodies, and/or combinations of the foregoing. The treatments are varyingly successful, dependent on the individual patient and disorder. However, a dilemma in the use of such general immunosuppressive therapies arises in that the greater the immune-suppression, and thus the increased potential for successful treatment of the autoimmune disorder, the more at-risk the patient becomes for developing opportunistic infections. Further, due to the compromised nature of the patient's immune system, even a minor infection can rapidly become of serious concern.
2.1.1 Diabetes
Diabetes is typically classified as one of two types: type 1 or type 2 diabetes. Type 2 diabetes is a non-autoimmune disease that is typically diagnosed in adults. It is a progressive disease that develops when the body does not produce sufficient insulin or fails to efficiently use the insulin it produces (a phenomenon known as insulin resistance). Patients diagnosed with type 2 diabetes are typically over age 45, overweight (BMI of 25 or higher) or obese (BMI of 30 or higher), physically inactive, have hypertension (blood pressure of 140/90 mm Hg or higher in adults), and have HDL cholesterol of 35 mg/dL or lower and/or triglyceride level of 250 mg/dL.
Type 1 diabetes, also known as juvenile diabetes or insulin-dependent diabetes mellitus, is an autoimmune disease that is typically diagnosed in children (although Adult-Onset type 1 diabetes may be present in adults). Insulin-dependent diabetes mellitus (IDDM) affects 15 million people in the United States with an estimated additional 12 million people who are currently asymptomatic, and, thus, unaware that they have this disease. Risk factors for developing type 1 diabetes include presumptive genetic factors, exposure to childhood viruses or other environmental factors, and/or the presence of other autoimmune disorders. Although the genetic factors associated with type 1 diabetes are not fully understood, risks for the development of the disease have been linked to both family history and ethnicity. For example, a child that has a parent or sibling with type 1 diabetes has a higher risk of developing type 1 diabetes than a child of non-diabetic parents or with non-diabetic siblings. Further, the genetic factors associated with the risk for developing type 1 diabetes appear to be linked to a particular HLA type: HLA-DR3 and DR4 are associated with a higher risk in Caucasians; HLA-DR7 is associated with a higher risk in people of African decent; and HLA-DR9 is associated with a higher risk in people of Japanese descent.
Unknown factors, including childhood viruses or exposure to some other environmental factor (e.g., exposure to certain foods or chemicals), are also theorized to potentiate or activate an inherited genetic factor and cause the onset of type 1 diabetes. Viruses that have been associated with type 1 diabetes include coxsackie B virus, enteroviruses, adenoviruses, rubella, cytomegalovirus, and Epstein-Barr virus. Last, the presence of other autoimmune disorders, such as thyroid disease and celiac disease, raises the risk of developing type 1 diabetes.
Type 1 Diabetes is caused by an autoimmune response in which the insulin producing β-cells of the pancreas (also known as islet cells) are gradually destroyed. The early stage of the disease, termed insulitis, is characterized by infiltration of leukocytes into the pancreas and is associated with both pancreatic inflammation and the release of anti-β-cell cytotoxic antibodies. As the disease progresses, the injured tissue may also attract lymphocytes, causing yet further damage to the β-cells. Also, subsequent general activation of lymphocytes, for example in response to a viral infection, food allergy, chemical, or stress, may result in yet more islet cells being destroyed. Early stages of the disease are often overlooked or misdiagnosed as clinical symptoms of diabetes typically manifest only after about 80% of the β-cells have been destroyed. Once symptoms occur, the type-1 diabetic is normally insulin dependent for life. The dysregulation of blood-glucose levels associated with diabetes can lead to blindness, kidney failure, nerve damage and is a major contributing factor in the etiology of stroke, coronary heart disease and other blood vessel disorders.
2.1.2 Multiple Sclerosis
Multiple sclerosis (MS) is a chronic, often disabling inflammatory disease of the central nervous system (CNS). MS is typified pathologically by multiple inflammatory foci, plaques of demyelination, gliosis, and axonal pathology within the brain and spinal cord. Although the causal events that precipitate the disease are unknown, converging lines of evidence suggest that the disease is caused by a disturbance in immune function. This disturbance permits cells of the immune system to attack myelin, the insulating sheath that surrounds the axons located in the CNS (i.e., the brain and spinal cord). When observed microscopically, plaques consist of inflammatory cells, astroglial cells, edema, and destroyed myelin fragments. When myelin is damaged, electrical impulses cannot travel quickly along nerve fiber pathways in the brain and spinal cord. Disruption of electrical conductivity results in fatigue and disturbances of vision, strength, coordination, balance, sensations, and bladder and bowel function. Thus, typical symptoms include one or more of weakness or paralysis in one or more extremities, tremor in one or more extremities, muscle spasticity, muscle atrophy, dysfunctional movement, numbness or abnormal sensation in any area, tingling, facial pain, extremity pain, loss of vision in one or both eyes, double vision, eye discomfort, uncontrollable rapid eye movements, decreased coordination, loss of balance, decreased ability to control small or intricate movements, walking or gait abnormalities, muscle spasms, dizziness, vertigo, urinary hesitancy, urinary urgency, increased urinary frequency, incontinence, decreased memory, decreased spontaneity, decreased judgment, loss of ability to think abstractly, loss of ability to generalize, depression, decreased attention span, slurred speech, difficulty speaking or understanding speech, fatigue, constipation, hearing loss, and/or positive Babinski's reflex. The symptoms recur periodically, last days to months, then reduce or disappear. With each recurrence, the symptoms may vary or be completely different as new areas are affected.
Studies of the natural history of MS suggest that there are different patterns of disease activity. Some patients have rare attacks, some have frequent attacks, and others gradually but steadily worsen without experiencing attacks. Patients who have rare attacks and are minimally disabled ten years after being diagnosed with MS are said to have benign MS. This group constitutes only about 10-15% of the total MS patient population, although there is some evidence suggesting that this course may be more common than is currently appreciated. Patients who have attacks with full or partial recovery and are otherwise stable between attacks are defined as having relapsing-remitting MS. Approximately 80-90% of patients with MS initially experience a relapsing-remitting course. Of these, approximately 50% will have difficulty walking 15 years after onset and 80% will ultimately (after about 25 years) experience gradual progression of disability with or without attacks. Patients who first experience exacerbations and later experience gradual progression of disability have secondary progressive MS. Approximately 10-15% of MS patients do not experience an initial attack. Those patients who gradually worsen after the appearance of the first symptom have primary progressive MS. A few patients with primary progressive MS will later experience an exacerbation. These patients have progressive-relapsing MS.
There is as yet no cure for MS. Many patients do well with no therapy at all, especially since many medications have serious side effects and some carry significant risks. However, three forms of beta interferon (AVONEX® (interferon beta-1a), BETASERON® (interferon beta-1b), and REBIF® (interferon beta-1a)) have now been approved by the Food and Drug Administration for treatment of relapsing-remitting MS. Beta interferon has been shown to reduce the number of exacerbations and may slow the progression of physical disability. When attacks do occur, they tend to be shorter and less severe. The FDA also has approved a synthetic form of myelin basic protein copolymer I, COPAXONE® (glatiramer acetate), for the treatment of relapsing-remitting MS. Copolymer I has few side effects, and studies indicate that the agent can reduce the relapse rate by almost one third. An immunosuppressant treatment, NOVATRONE® (mitoxantrone), is also approved by the FDA for the treatment of advanced or chronic MS.
2.2 T Cell Functionality in Diabetes and Other Autoimmune Disorders
Destruction of β-cells in diabetes, of myelin in multiple sclerosis, or of the target cells of other autoimmune disorders is believed largely mediated by cytotoxic T-lymphocytes (CTLs—also known as CD8+ T cells) that specifically recognize antigenic, target cell derived peptides. CTLs, as well as other types of T cells, recognize these antigenic peptides through their specific T cell receptor (TcR). Unlike antibodies which recognize soluble whole foreign proteins as antigen, the TcR instead interacts with small peptidic antigens presented only in complex with major histocompatibility complex (MHC) proteins.
Most cells of the body express MHC molecules of various classes on their surface and, depending on the class of MHC expressed, will present either soluble antigens, those dispersed within the lymph and/or circulatory systems, or fragments of their cytoplasmic proteins. MHC molecules (called human leukocyte antigens or HLA in humans) and TcRs are extremely polymorphic, each clonal variation recognizing and binding to a single peptidic sequence, or set of similar peptidic analogs. Apart from cells specific to the immune system, i.e. B cells and T cells, cells of the body express multiple variants of the MHC molecule, each variant binding to a different peptide sequence. In contrast, during maturation, B and T cells lose the ability to express multiple variants of MHC and TcR, respectively. Mature T cells, therefore, will express only one of the possible variants of the TcR and will thus recognize/bind a single MHC/antigen complex.
Binding of a TcR to a MHC/antigen complex elicits an intracellular signal cascade within the T cell, termed activation, which results in clonal proliferation of the T cell and class-specific T cell responses. For example, in CTLs the response to activation also includes the release of cytotoxic enzymes that result in apoptosis/destruction of the target cell.
2.3 Modulation of T Cell Activation by Monoclonal Antibodies
The finding that autoimmune diseases are at least partially caused by aberrant T cell action has lead to the investigation of therapies that either eliminate problematic T cell clones (those expressing TcRs against self antigens) or selectively reduce undesired T cell activity/activation. T cell activation due to TcR binding is, however, an unexpectedly complex phenomenon due to the participation of a variety of cell surface molecules expressed on the responding T cell population (Billadeau et al., 2002, J. Clin. Invest. 109:161-168; Weiss, 1990, J. Clin. Invest. 86:1015-1022; Leo et al., 1987, PNAS 84:1374-1378; Weiss et al., 1984, PNAS 81:4169-4173; Hoffman et al., 1985, J. Immunol. 135:5-8).
Targeted therapies directed against general T cell activation were problematic in that the TcR is composed of a disulfide-linked heterodimer, containing two clonally distributed, integral membrane glycoprotein chains, α and β, or γ and δ. Most of the research in modulation of T cell activation was done in connection with improving immune suppression in organ transplant recipients. One of the first clinically successful methods of selectively reducing T cell activation was the use of monoclonal antibodies. U.S. Pat. No. 4,658,019, describes a novel hybridoma (designated OKT3, ATCC Accession No. CRL-8001) which produces a murine monoclonal antibody against an antigen found on essentially all normal human peripheral T cells. Binding of OKT3 to T cells in vivo produces pronounced, reversible immunosuppression. OKT3 was found to recognize an epitope on the 8-subunit within the human CD3 complex (Salmeron et al., 1991, J. Immunol. 147:3047-3052; Transy et al., 1989, Eur. J. Immunol. 19:947-950; see also, U.S. Pat. No. 4,658,019). The CD3 complex (also known as T3) is comprised of low molecular weight invariant proteins, which non-covalently associate with the TcR (Samelson et al., 1985, Cell 43:223-231). The CD3 structures are thought to represent accessory molecules that may be the transducing elements of activation signals initiated upon binding of the TcR α-β to its ligand.
OKT3 possesses potent T cell activating and suppressive properties (Van Seventer, 1987, J. Immunol. 139:2545-2550; Weiss, 1986, Ann. Rev. Immunol. 4:593-619). Fc receptor-mediated cross-linking of TcR-bound anti-CD3 mAb results in T cell activation marker expression, and proliferation (Weiss et al., 1986, Ann. Rev. Immunol. 4:593-619). Similarly, in vivo administration of OKT3 results in both T cell activation and suppression of immune responses (Ellenhorn et al., 1990, Transplantation 50:608-12; Chatenoud, 1990, Transplantation 49:697). Repeated daily administration of OKT3 results in profound immunosuppression, and provides effective treatment of rejection following renal transplantation (Thistlethwaite, 1984, Transplantation 38:695).
The use of therapeutic mAbs, including, for example, OKT3, is limited by problems of “first dose” side effects, ranging from mild flu-like symptoms to severe toxicity. The first dose side effects are believed to be caused by cytokine production stimulated by T cell activation. It has been shown that the activating properties of Anti CD3 monoclonal antibodies result from TcR cross-linking mediated by the antibodies bound to T cells (via its variable domain) and to FcγR-bearing cells via its Fc domain) (Palacios et al., 1985, Eur. J. Immunol. 15:645-651; Ceuppens et al., 1985, J. Immunol. 134:1498-1502; Kan et al., 1986, Cell Immunol. 98:181-185). For example, the use of OKT3 was found to trigger activation of mAb-bound T cells and FcγR-bearing cells prior to achieving immune suppression, resulting in a massive systemic release of cytokines (Abramowicz, 1989, Transplantation 47:P606; Chatenoud, 1989, N. Eng. J. Med. 25:1420-1421). Reported side effects of OKT3 therapy include flu-like symptoms, respiratory distress, neurological symptoms, and acute tubular necrosis that may follow the first and sometimes the second injection of the mAb (Abramowicz, 1989, Transplantation 47:P606; Chatenoud, 1989, N. Eng. J. Med. 25:1420-1421; Toussaint, 1989, Transplantation 48:524; Thistlethwaite, 1988, Am. J. Kid. Dis. 11:112; Goldman, 1990, Transplantation 50:148).
Data obtained using experimental models in chimpanzees and mice have suggested that preventing or neutralizing the cellular activation induced by anti-CD3 mAbs reduces the toxicity of these agents (Parleviet, 1990, Transplantation 50:889; Rao, 1991, Transplantation 52:691; Alegre, 1990, Eur. J. Immunol. 20:707; Alegre, 1990, Transplant Proc. 22:1920; Alegre, 1991, Transplantation. 52:674; Alegre, 1991, J. Immun. 146:1184-1191; Ferran, 1990, Transplantation 50:642). Previous results reported in mice using F(ab′)2 fragments of 145-2C11, a hamster anti-mouse CD3 that shares many properties with OKT3, have suggested that, in the absence of FcγR binding and cellular activation, anti-CD3 mAbs retain at least some immunosuppressive properties in vivo (Hirsch, 1991, Transplant Proc. 23:270; Hirsch, 1991, J. Immunol. 147:2088). In addition, administration of anti-CD3 antibodies with reduced binding to FcγR to human patients resulted in generally only mild side effects and not the severe first class effects associated with OKT3 administration (Herold et al., 2005, Diabetes 54:1763).
2.4 Immunosuppressive Monoclonal Antibodies Exhibiting Reduced T Cell Activation
U.S. Pat. No. 6,491,916, U.S. Pat. Application Pub. No. 2005/0064514 and U.S. Pat. Application Pub. No. 2005/0037000 describe the modification of the Fc regions of immunoglobulins such that the variant molecules exhibit enhanced or reduced binding to various Fc receptors when compared to immunoglobulins with wild type Fc domains. In particular the patents/applications describe modifications to the Fe regions of IgG antibodies such that the affinity for the FcγR is selectively enhanced or reduced. By tailoring the affinity for activating or suppressive Fc receptors, the specific immune response elicited by the therapeutic mAb may be more selectively controlled. For example, mutations in the CH2 portion of a humanized OKT3 IgG4 have been identified (P234A and L235A) that significantly reduced binding of the mAb to human and murine FcγRI and II and lead to a markedly reduced activating phenotype in vitro (Alegre et al., 1992, 8th International Congress of Immunology 23-28; Alegre et al., 1994, Transplantation 57: 1537-1543; Xu et al., 2000, Cell Immunol. 200:16-26). Importantly, this variant mAb retained the capacity to induce TcR modulation and immunosuppression (Xu et al., 2000, Cell Immunol. 200:16-26). Other modifications to the Fe domain of anti-CD3 antibodies, such as mutations to make the antibody aglycosylated or other mutations of the Fe domain residues, to reduce binding to FcγR have been found to reduce toxicity while maintaining immunosuppressive activity (see, e.g., U.S. Pat. No. 6,491,916; U.S. Pat. No. 5,834,597, Keymeulen et al., 2005, N. Eng. J. Med. 325:2598, all of which are incorporated by reference herein in their entireties).